1. Field of the Invention
The present invention is directed to a current limiting circuit breaker with an arc shearing plate which is controlled to move into a position for rapid extinction of an arc formed between contacts being separated upon the occurrence of a predetermined over-current condition.
2. Information Disclosure of the Prior Art
A circuit breaker with an arc shearing plate is already known in the art, as disclosed in the following U.S. patents:
(1) U.S. Pat. No. 3,842,228;
(2) U.S. Pat. No. 4,467,298; and
(3) U.S. Pat. No. 4,562,323.
The patent (1) discloses a circuit breaker in which a wedge member of dielectric material is controlled by a solenoid to thrust between a pair of electrical contacts for opening the contacts and at the same time shearing the arc formed between the contacts.
The patent (2) discloses a circuit breaker in which an arc shearing plate is spring biased to thrust between a pair of electrical contacts as soon as the contacts are electromagnetically repelled to its open position.
The patent (3) discloses a circuit breaker in which an arc shearing plate is controlled by a solenoid to thrust between a pair of electrical contacts after the contacts are driven to move its open position by a control means which is a separately mounted from the solenoid and operates independently thereof.
In the circuit breakers according to the above patents (1) and (2), the arc shearing plate suffers from high frictional forces as it moves to a position of interposing itself between the contacts due to the wedge engagement of the arc shearing plate with the contacts. The high frictional forces inevitable with this type of circuit breaker will retard the movement of the plate and consequently require a relatively longer time for shearing an arc formed between the contacts being separated.
In the circuit breaker according to the above patent (3), the arc shearing plate and the contacts are controlled by individual control means, i.e., respectively by the electromagnet and another fault-current responsive member provided separately therefrom. Although this provision of separate control means is effective for obtaining rapid movement of the arc shearing plate to its interposed position between the contacts, it requires duplication of the fault-current responsive members with the consequent difficulty in controlling to match the timing of inserting the plate to that of separating the contacts. This makes it difficult to obtain an optimum operating characteristic of the arc shearing plate which is to be determined in close association with the contact separation. In this sense, none of the prior circuit breakers shows the use of a single over-current responsive actuator as a common member for controlling the contact separation as well as for thrusting of the arc shearing plate between the contacts in a synchronized sequence.